I wonder if you find them flat because they are older. Youth has a way of being more dramatic because it has more possibilities and less cynicism. But I think that is what is interesting about having sort of both trilogies. You see how when people get older they become more stubborn and close minded.

I personally don't really care if there is a sequel to one or the other as long as it is good. But the question was rather see. I would rather see an X4 based almost solely on the fact that there are better characters from the comics in the original trilogy. I love Magneto but he isn't the only character I want developed.

as far as what I want to see out of a future X-men movie? Don't have any larger plot ideas and none of these are exclusive to either an X4 or First Class sequel (on a side note, lets not call it second class, that just draws attention to its lack of power players and would be way too easy for a reviewer to make jokes.) But I would like to see:

Sentinels as a villain. Obvious chance for a true team battle, (see incredibles)

and I want to see more young mutants (or mutants in general) trying to live in the real world with the more basic prejudices they face. It doesn't always have to be about mass extinction. Teen angst gets annoying, but when its someone like Rogue its pretty hard not to sympathize. I would like to see more day to day stuff outside the mansion.

Also I think having characters like Pietro and Wanda dealing with a deranged super villain father could make for a new interesting dynamic. (not sure how this would work in the movieverse though)

If its a first class sequel, going back to my first sentence a little bit I really want to have more of a sense of young people really wanting to change the world. For some reason watching First Class it didn't seem all that hopeful for the future. I want these characters to be a bit more optimistic and not just naive. Really fight for their beliefs in a better future.